Light is formed of waves that vibrate in a transverse direction in the plane of the wave front. As light propagates in a direction, the wave front also propagates in that direction. Elliptical vibration is the most general case, and linear and circular vibrations are specific cases. The present invention relates to plane-polarized light (sometimes referred to as linear polarized light) wherein the wave vibrations are in a single plane. The plane polarized light may be used to create elliptically or circularly polarized light. The plane polarized light and/or circularly polarized light may be used in a variety of devices and methods, such as displays, shutters, optical (e.g., light) protection devices, special viewing devices, etc. Further description of polarized light and prior techniques for obtaining polarized light is provided in Fundamentals of Optics, (Jenkins and White, McGraw-Hill, Inc., New York, 1976), for example at chapters 24-26, the entire disclosure of which hereby is incorporated by reference.
Several methods for producing plane-polarized light described in Jenkins and White include reflection, transmission through a pile of plates, dichroism, double refraction, and scattering. Use of liquid crystal material to affect polarization and/or to polarize light is mentioned in U.S. Pat. Nos. 4,048,358, 4,688,900, and 4,685,771, and PCT patent application Publication No. WO 90/04805.
In the mentioned patents and published patent application polarization occurs as the light travels through the liquid crystal material and/or dye, e.g., pleochroic dye, contained in the liquid crystal material. However, due to uncontrolled scattering of at least some of the light, efficiency of polarization is reduced from the maximum.
A polarizer on demand device responds to a prescribed input or condition to polarize light or to reduce polarization of light, e.g., to be in a clear or substantially fully light transmissive state. As is described in the above PCT application Publication No. WO 90/04805, application of electric field reduces or stops polarization of light so that light is transmitted without regard to polarization direction; and removal of the field causes an increase in the polarization of transmitted light.
Reference is made to an article by M. F. Webber entitled "Retroreflecting Sheet Polarizer" published in the SID 93 Digest at page 669 on May 18, 1993. A reflecting sheet polarizer of a microprism array with thin film optical stacks is described in that paper. The device works generally according to Brewster's law so that s-polarized light, e.g., one polarized component--meaning plane polarized light, is reflected and p-polarized light, e.g., the other, i.e., relatively orthogonal, polarized component, is transmitted.
A stamped morphology technique for making a liquid crystal device is described in a paper entitled--Control of the LC Alignment Using a Stamped Morphology Method and its Application to LCDs" by Lee et al., SID 93 Digest at page 957, published May 18, 1993. This paper describes a method of aligning liquid crystal using microgrooves formed by a stamping process. Pretilt angle and azimuthal surface anchoring energy are described. Other exemplary techniques currently used for aligning liquid crystal material include rubbing of a surface and depositing of an evaporated coating. In one example of a rubbing technique, a surface intended to be in engagement with the liquid crystal material may be rubbed in a particular direction using a fabric material; often the surface first is coated with a material, such as polyvinyl alcohol or some other alignment material, which is rubbed. In the deposition technique, a material, such as a silicon oxide or silicon dioxide, is evaporated using known techniques and is deposited onto the surface that is to be engaged with the liquid crystal material; such deposition is carried out while the surface is maintained at a prescribed orientation relative to the evaporated material. Other techniques for aligning liquid crystal also may be used.
Several of the types of the liquid crystal materials currently known include those categorized as nematic, smectic, and cholesteric. Nematic liquid crystal tends to have a structural arrangement, alignment, or organization that tends to be linear, and the linear alignment thereof, or of the molecular or optical axis thereof often is referred to direction-wise with reference to the director of the nematic liquid crystal. Nematic liquid crystal tends to have directional alignment characteristics with respect to other nematic liquid crystal whereby the liquid crystal structure or directors tend to align in parallel, but nematic liquid crystal tends not to have a positional alignment requirement. In contrast, smectic liquid crystal, which has directional alignment characteristics, also tends to have positional alignment characteristics. Thus, smectic liquid crystal tends to orient in a layered arrangement or structure. Cholesteric liquid crystal material tends to have a helical or twisted structure.
Liquid crystal materials, such as nematic liquid crystal and smectic liquid crystal, often are anisotropic; for example, they may be optically anisotropic and/or electrically anisotropic. Nematic liquid crystal or smectic liquid crystal that has the characteristic of optical anisotropy, has an ordinary index of refraction experienced or measured when looking, traveling or propagating along the axis or the direction of the director of the liquid crystal and a different extraordinary index of refraction, which is experienced or measured when looking, travelling or propagating in a direction that is perpendicular to the axis or direction of the director for light that is vibrating in a plane that is congruent or coplanar with the liquid crystal axis or direction of the director. For light that is propagating in a direction perpendicular to the liquid crystal optical axis in a plane that is perpendicular to a plane that is congruent with the liquid crystal axis, the ordinary index of refraction characteristic of the liquid crystal is experienced.